5Speed of Sound Depends on the medium. The more elastic the medium the faster sound will travel through it. Speed in metals>speed in water>speed in airSound can’t travel through vacuum.
6Speed of Sound in Air v = 331 + 0.6 T ( in meters/sec) T is the temperature in 0C.In higher humidity, sound will travel faster.For 15°C, v = *15 = 340 m/sUse 340 m/s as an average speed of sound in air.
7Faster than the speed of Sound Supersonic – motion faster than speed of soundSonic boom – caused by an object breaking the sound barrier (supersonic planes, bullets)
8Plane reaches speed above 770 mph – Explosion of sound waves caused by air crashing behind the plane The air can condense or sweep up vapor from engine – causing this picture
9Pitch: the frequency of a sound wave. Musical notes have a given pitch.The note C has a frequency of 327Hz.When two notes differ by a ratio of 2:1 they are one octave apart.What would be the next higher C? (Ans:654Hz)
10Pitch – frequency of sound wave Humans can hear frequencies between 20 Hz and 20,000 HzInfrasonic frequencies: Below 20 Hzused by elephants and submarines to communicate over long distancesUltrasonic frequenciesDog whistles
11Loudness = Amplitude Loudness is measured in decibels (dB) A +10 dB change we hear as twice as loudA -10 dB change we hear as half as loud
12Decibels – Loudness measure EXAMPLE: If a sound is 20 dB loud, answer how many dB these would be:A sound twice as loud:A sound half as loud:A sound three times as loud:30 dB10 dB35 dB
14Examples of Sound Intensity Levels jet plane taking off dBair raid siren dBthreshold of pain dBloud rock music dBear damage starts dBbusy traffic dBnormal conversation dBquiet library dBsoft whisper dBthreshold of human hearing dB
15Timbre – tone qualityWhat makes a particular musical sound different from another, even when they have the same pitch and loudnessEX: difference between a guitar and a piano playing the same note at the same loudnessSounds can be described in terms of “coloration,” e.g. bright, dark, warm, harsh, etc.
16Timbre – tone qualityColor of the note is due to the presence of different harmonics.The “oo” has mostly low harmonics, while the “ee” has mostly high harmonics
17Harmonics - Reviewv = λ f - The velocity of the wave stays the same, even if considering different harmonics….it’s still the same wave!!!
19Properties of Sound Reflection (Echo) Refraction Interference Diffraction
20EchoesEchoes are sounds that are reflected back by a hard boundary.
21EchoesEcholocation – used by many animals like bats to see through dark water or at nightSonar – sound through waterRadar – light waves through airSonograms – sound waves through the human body
22Beats Interference effect When two waves of close frequencies interact causing alternating constructive and destructive interference
23BeatsThe number of beats = difference of two frequencies (absolute value)EX: f1 = 345 Hz; f2 = 342 HzNumber of beats = 345 – 342 = 3There will be three beats per secondchampions.com/science/sound_beat_frequencies.htm#.U2gpwletJW8
24Bow (Shock) WavesWhen the speed of a moving sound source is greater than the speed of the wave, a pressure ridge builds similar to the wave created by the bow of a ship.physlet animation
25Sonic BoomWhen the pressure ridge of a bow wave of a jet passes over an observer on the ground, the observer experiences a sonic boom.
26Doppler EffectThe change in a wave's perceived frequency due to the motion of either the sound source or the observer. It is applicable to any type of wave.Austrian physicist Christian Doppler ( ).train sound clipSimulationsphyslet animation
28The Doppler EffectIn front of the source the sound waves are compressed (shorter wavelength λ) and this raises the frequency (pitch)Behind the source the sound waves are stretched (longer wavelength λ) and this drops the frequency (pitch)Anything moving at the same speed as the source will experience no change in frequency